This application applies generally to the field of metallurgy, and more specifically to the manufacturing and repair of alloy articles, and in particular, to the manufacturing and repair of a superalloy component of a gas turbine engine.
High temperature cobalt-based and nickel-based superalloys are commonly used in the manufacture of gas turbine engine components, including combustors, rotating blades and stationary vanes. During the operation of these components in the harsh operating environment of a gas turbine, various types of damage and deterioration of the components may occur. For example, the surface of a component may become cracked due to thermal cycling or may be eroded as a result of impacts with foreign objects and corrosive fluids. Furthermore, such components may be damaged during manufacturing operations even prior to entering service. Because the cost of gas turbine components made of cobalt-base and nickel-base superalloys is high, repair of a damaged or degraded component is preferred over replacement of the component.
Several repair techniques have been developed for various applications of superalloy materials. Fusion welding of superalloy materials is known to be a difficult process to control due to the tendency of these materials to crack at the area of the weld site. However, with careful pre-weld and post-weld stress relief, control of welding parameters, and selection of welding materials, repair welds can be performed successfully on superalloy components.
Brazing is also commonly used to join or to repair superalloy components. One limitation of brazing is that brazed joints are typically much weaker than the base alloy, and so they may not be appropriate in all situations, such as repairs on the most highly stressed areas of the component.
Another process that has been used successfully for repair and material addition to superalloy components is known by several different names: diffusion bonding; diffusion brazing; and liquid phase diffusion sintering. These names generally refer to a process wherein a powdered alloy is melted at a temperature that is less than the liquidous temperature of the base alloy and allowed to solidify to become integral with the component. The powdered alloy typically includes particles of a high strength alloy, for example the same alloy as is used to form the base component, along with particles having a lower melting temperature than the high strength alloy, for example the base alloy with a melting point depressant such as boron. The component and powder are subjected to a heat cycle, often called a brazing heat treatment, wherein the temperature is selected so that the braze material having a lower melting temperature will become liquid and will wet the surfaces of the high melting temperature particles and base alloy. The component is held at this elevated temperature for a sufficient interval to promote liquid phase sintering. Liquid phase sintering is a process whereby adjacent particles in a powder mass are consolidated by diffusion through a liquid phase present between the particles. This diffusion process is also known as sintering. As the melting point depressant diffuses away from the braze area, the liquid material will solidify to form the desired joint or material addition to the component. A further post-braze diffusion heat treatment may be applied at a somewhat lower temperature to further drive the melting point depressant away from the braze and to more fully develop the desired material properties. Such a liquid phase diffusion bonding process is capable of forming a joint with material properties approximating those of the base alloy.
The cost of manufacturing and repair of a superalloy component is directly related to the time necessary to accomplish the manufacture or repair. The various thermal processes necessary to develop the desired material properties in a superalloy component all require a significant amount of time, ranging form a few hours to a day or more for each heat cycle. These thermal processes may include an original manufacturing solution heat treatment performed after the material is cast, a pre-weld heat treatment, a post-weld heat treatment, a brazing heat treatment for liquid phase diffusion bonding, and a post-brazing diffusion heat treatment. A method that reduces the time necessary for manufacturing or repair of a superalloy component is needed.
A method for manufacturing a gas turbine component is described herein as including: casting an alloy material to form a component; performing a solution heat treatment on the component; subjecting the component to an operating environment; applying an alloy powder mixture to the component; and bonding the alloy powder mixture to the component by liquid phase diffusion bonding using a brazing heat treatment that incorporates the solution heat treatment, the alloy powder mixture selected to achieve a desired material property when exposed to the brazing heat treatment. In one embodiment, the alloy material is selected to be IN 939; the alloy powder mixture is selected to be a 50/50 ratio by weigh percent of IN 939 and AM 775 alloys; the solution heat treatment is performed as heating the component to 2,120xc2x0 F. for four hours followed by cooling to below 1,000xc2x0 F. in twenty minutes or less; and the brazing heat treatment cycle is performed as heating the component to 2,120xc2x0 F. for four hours, cooling the component to 2,050xc2x0 F. and holding for four hours, followed by cooling from 2,050xc2x0 F. to below 1,000xc2x0 F. in twenty minutes or less.
A method is further described as including: casting an alloy material to form a component; applying an alloy powder mixture to the component; and performing a solution heat treatment cycle on the component, the solution heat treatment cycle functioning as a brazing heat treatment for bonding the alloy powder mixture to the component by liquid phase diffusion bonding, the powder mixture selected to achieve a desired material property when subjected to the solution heat treatment cycle.
In another embodiment, a method of repairing a component is described as including: applying a first alloy powder mixture to a component formed of an alloy material; bonding the first alloy powder mixture to the component by liquid phase diffusion bonding using a first brazing heat treatment that accomplishes bonding between the first alloy powder mixture and the component by liquid phase diffusion bonding and that also accomplishes a pre-weld stress relief in the component; and performing a welding process on the component after the step of bonding.
A method is also described as including the steps of: performing a welding process on a component formed of an alloy material; applying an alloy powder mixture to a portion of the component; and bonding the alloy powder mixture to the component by liquid phase diffusion bonding using a brazing heat treatment that accomplishes liquid phase diffusion bonding between the alloy powder mixture and the component and that also accomplishes a post weld stress relief in the component. In one embodiment, the brazing heat treatment may be selected to incorporate a manufacturing solution heat treatment used to form the component.